Low-cost green smelting method for hot work die steel

Abstract

The invention relates to a low-cost green smelting method for hot work die steel, and belongs to the technical field of electric arc furnace steelmaking in the metallurgical industry. According to the technical scheme, the burdening structure of the electric arc furnace steelmaking procedure comprises 15%-20% of hydrogen-based DRI and 80%-85% of waste steel, 40%-50% of hydrogen-based DRI is added along with the waste steel, the remaining hydrogen-based DRI enters an oxidation period and then is sequentially added into a furnace in batches, the content of C at the end point of molten steel is controlled to be larger than or equal to 0.10%, the content of P is smaller than or equal to 0.004%, the content of S is smaller than or equal to 0.015%, and finally 0.5-1.0 kg / t of carbon powder is sprayed on the slag surface; and in the refining process, the Al content is controlled to be greater than or equal to 0.030 wt% and the S content is less than or equal to 0.005 wt% The method has the beneficial effects that slag carried by molten steel during tapping and pollution caused by large rephosphorization amount can be reduced, and meanwhile, the hydrogen-based DRI raw material is adopted to replace part of waste steel, so that the cleanliness of the molten steel is improved.

Description

Technical Field

[0001] The invention relates to a low-cost green smelting method for hot-working die steel, belonging to the technical field of electric arc furnace steelmaking in the metallurgical industry. Background Art

[0002] At present, there are still some non-combined electric arc furnace production enterprises under traditional process conditions in China, and their steelmaking production mode belongs to the short process of non-iron addition. Although in recent years, some refining process equipment outside the furnace has been added to improve the reduction period of smelting, due to historical reasons, the furnace type of some enterprises' electric arc furnaces still belongs to the "old three phases" form. The so-called "old three phases" furnace type is a non-eccentric furnace body steel structure with a steel trough, that is, a steel outlet with a steel trough. Slag discharge is a problem that plagues this type of enterprise. In addition, the current domestic scrap steel resource processing conditions are poor, and social scrap steel lacks a sound classification identification and differentiation method, making it difficult to achieve deep purification of molten steel, which restricts the production of short-process high-performance steel materials.

[0003] High-end mold steel varieties require lower sulfur, phosphorus content, nitrogen, oxygen gas, and B and D inclusion levels, so the electric arc furnace needs to maintain a high decarburization amount to remove impurities and P and S content in the molten steel. In the production enterprises of all-scrap steel electric arc furnaces, if pig iron is used as the carbon raw material during batching, the source of pig iron is uncontrollable, and P, S and other impurities such as As and Sn are high, resulting in poor stability of the electric arc furnace process and poor control of the smelting endpoint, which also restricts the stability of the purity of the mold steel. Summary of the invention

[0004] The purpose of the present invention is to provide a low-cost green smelting method for hot working die steel, which can reduce the pollution caused by slag in molten steel and large amount of phosphorus regeneration during steel tapping, and at the same time use hydrogen-based DRI raw materials to replace part of the scrap steel to improve the cleanliness of the molten steel, thereby solving the problems existing in the background technology.

[0005] The technical solution of the present invention is:

[0006] A low-cost green smelting method for hot-working die steel comprises an electric arc furnace steelmaking process, a refining process and a die casting process. The batching structure of the electric arc furnace steelmaking process is as follows: 15% to 20% hydrogen-based DRI and 80% to 85% scrap steel, wherein 40% to 50% of the hydrogen-based DRI is added with the scrap steel, and the remaining hydrogen-based DRI is added to the furnace in batches after entering an oxidation period, so that the C content of the molten steel endpoint is controlled at ≥0.10%, P≤0.004%, and S≤0.015%, and finally 0.5 to 1.0 kg / t of carbon powder is sprayed on the slag surface; in the refining process, LF outgoing Al is controlled at ≥0.030wt% and S≤0.005wt%.

[0007] The electric arc furnace steelmaking process: when the electric arc furnace is tapping steel, when the furnace body reaches the limit tilting angle, the maximum angle α between its tapping channel and the horizontal line is -30°.

[0008] The maximum tilting angle of the furnace body is 45°.

[0009] The refining process: relying on SiC and aluminum particles for diffusion deoxidation to form white slag, the white slag period is not less than 20 minutes, the binary basicity of LF refining slag is 3.5-5.5, VD vacuum treatment is 10-12 minutes, and the molten steel is left standing for 10-20 minutes.

[0010] In the refining process, the amount of SiC added is 3.0-4.0 kg / t, and the amount of aluminum particles added is 2.0-3.0 kg / t.

[0011] The mold casting process: the surface temperature of the outer wall of the steel ingot mold is greater than 80°C before pouring.

[0012] The beneficial effects of the present invention are as follows: without changing the existing arc furnace structure and other electronic controls, slag is controlled as much as possible, and the pollution caused by slag in molten steel and large amount of phosphorus regeneration during steel tapping is reduced from the source. At the same time, hydrogen-based DRI raw materials are used to replace part of the scrap steel to improve the cleanliness of the molten steel, so that the mold steel produced has higher purity, and the high-temperature thermal stability and fatigue resistance meet the needs of customers. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of the furnace body tapping port channel bricks added by the present invention;

[0014] Figure 2 It is a cross-sectional schematic diagram of an arc furnace body of the present invention;

[0015] Figure 3 This is a schematic diagram of the steel-making process of the electric arc furnace of the present invention;

[0016] In the figure: electric arc furnace wall bricks 1, molten steel channel bricks 2, electrodes 3, steel tapping channel 4, steel slag 5, molten steel 6, electric arc furnace body 7. DETAILED DESCRIPTION

[0017] The present invention will be further described below by way of examples with reference to the accompanying drawings.

[0018] See attached Figure 1-3A low-cost green smelting method for hot-working die steel comprises an electric arc furnace steelmaking process, a refining process and a die casting process. The batching structure of the electric arc furnace steelmaking process is: 15% to 20% hydrogen-based DRI and 80% to 85% scrap steel, wherein 40% to 50% hydrogen-based DRI is added with the scrap steel, and the remaining hydrogen-based DRI is added to the furnace in batches after entering the oxidation period, so that the C content of the molten steel end point is controlled at ≥0.10%, P≤0.004%, and S≤0.015%, and finally 0.5 to 1.0 kg / t carbon powder is sprayed on the slag surface; in the refining process, the LF outgoing Al is controlled at ≥0.030wt% and S≤0.005wt%.

[0019] The present invention is particularly aimed at the "old third phase" furnace type, and the steel tapping structure is a non-eccentric furnace body steel tapping structure with a steel tapping trough body. Figure 1-3 , the form of the arc furnace tapping port base brick 4 is innovatively optimized, and the arc furnace tapping port base brick channel 2 is transformed from an angle of 0° with the horizontal to an angle of 15° with the horizontal with an upward inclination; the upper part of the tapping channel 2 is a circular arch channel refractory. As the arc furnace body shakes and taps steel, the angle α between the channel and the horizontal line is constantly decreasing. Since the arc furnace body 7 has a maximum tilting angle of 45°, when tapping steel, when the furnace body 7 reaches the maximum tilting position of -45°, the actual maximum angle α between the channel 2 and the horizontal line is -30°. Under the same loading amount, the height of the remaining molten steel 6 in the furnace body is higher than before the transformation, the amount of slag 5 swirling into the tapping port is controlled, and the remaining slag at the bottom of the furnace is discharged regularly.

[0020] The low-cost green smelting process of the mold steel includes electric arc furnace steelmaking, LF refining, VD vacuum refining, die casting, pit cooling and hot delivery, among which:

[0021] (1) Electric arc furnace steelmaking: The batching structure includes 10% to 20% hydrogen-based DRI and 80% to 85% scrap steel, of which 40% to 50% of the DRI raw material is added with scrap steel, taking advantage of its high carbon content and low sulfur, phosphorus and other impurity elements. Due to the slag making and slagging during the dephosphorization period, DRI is lost with the slag after oxidation. After entering the oxidation period, the remaining DRI pellets are added to the furnace in batches according to the foaming degree of the foam slag, which can keep the molten steel with a continuous submerged arc foam slag effect. And the C content of the molten steel endpoint is controlled at ≥0.10%, P≤0.004%, S≤0.015%; after the endpoint sample is tested and qualified, the temperature is raised to meet the process requirements, 0.5-1.0kg / t carbon powder is sprayed on the slag surface to thicken the final slag, and ferromolybdenum is added in the furnace before power outage, and then the power is turned off and the furnace is shaken to tap steel. When tapping steel from the electric arc furnace, 5.0-10.0kg / t of Si iron is pre-deoxidized in the ladle to reduce the activity of oxygen, and then 0.5-1.0kg / t of AL is added, and 5.0-10.0kg / t of pre-melted refined slag is added with the steel flow, and alloying of the tapped steel is performed according to the actual situation;

[0022] (2) Refining process (LF+VD): LF outgoing Al is controlled at ≥0.025wt%, S≤0.005wt%, and other components are controlled in accordance with the requirements of the operating instructions. The aluminum supplementation operation is required to be completed before the middle of LF refining; SiC and aluminum particles are diffused and deoxidized to form white slag. The amount of SiC added is 3.0-4.0kg / t, and the amount of aluminum particles added is 2.0-3.0kg / t, which is controlled according to the slag situation of the electric arc furnace. The white slag period is not less than 20 minutes, and the binary basicity of LF refining slag is 3.5-5.5. Calcium treatment is prohibited during refining; after the VD vacuum treatment for 12 minutes, ensure that the ladle is soft-blown for 15 minutes or more, and increase the standing time of the molten steel by 10-20 minutes. The amount of argon gas blown at the bottom during refining is controlled in accordance with the requirements of the operating instructions.

[0023] (3) Mold casting process (MC): Before the ladle is hoisted to the steel casting platform, the mold casting system is fully equipped with the conditions for pouring. The pouring method is adopted to establish a full range of argon protection system. First, the argon at the inlet of the middle injection pipe is replaced by the casting system 3 minutes before pouring (50-100NL / min). There is an argon isolation device between the ladle water outlet and the steel pouring port of the middle injection pipe to form an argon ring to surround the steel flow. Finally, a small amount of argon is also sealed at the top of the ingot mold during the steel casting process (10-30NL / min). The amount of gas should not affect the coverage of the protective slag on the molten steel. The surface temperature of the outer wall of the ingot mold is greater than 80℃. The drainage sand is discharged before pouring. The ingot casting, riser shrinkage compensation time and the amount of protective slag used are controlled according to the requirements of the operation instructions. After slow cooling in the pit for 2-3 hours, the insulated car is sent to the heating furnace of the forging process for demolding and heating. The surface temperature of the demolding mold casting is maintained at ≥790℃.

[0024] Taking the production of H13 mold steel series as an example, the standard requirements for its main chemical (melting) components are (wt): C 0.38%~0.41%, Si 0.90%~1.10%, Mn 0.30%~0.40%, P≤0.015%, S≤0.005%, Cr5.10%~5.20%, Mo1.25~1.35%, V 0.95~1.05%, Al 0.010~0.030%, of which the balance is Fe and unavoidable impurities.

[0025] (1) Electric arc furnace production process control:

[0026] The ingredients include 10% to 20% hydrogen-based DRI and 80% to 85% scrap steel. The ingredient structure is shown in Table 1. Among them, 50% of the DRI raw material is added with the scrap steel, and the remaining 50% DRI is gradually added to the furnace after entering the oxidation period to maintain a continuous submerged arc foam slag effect. The C content of the molten steel endpoint is controlled at ≥0.10%, P≤0.004%, S≤0.015%, and the endpoint composition and temperature are shown in Table 2. The electric arc furnace is shaken to tap the steel at an angle of 45° to the horizontal, and the tapping is completed. During this period, a two-step deoxidation method is used in the ladle, first with ferrosilicon pre-deoxidation and then with aluminum deoxidation. 10kg / t of pre-melted refined slag is added to the ladle with the steel flow. The ladle charging is shown in Table 3.

[0027] Table 1: Raw material structure of furnace

[0028] Example DRI kg White ash kg Fluorite kg Scrap steel kg 1 1360 500 100 8350 2 1450 500 80 9430 3 1610 500 100 9130 4 1824 500 100 8444 5 1530 500 100 8960

[0029] Table 2: Steel tapping end point composition temperature control

[0030] Example C％ P％ S％ Temperature ℃ 1 0.12 0.002 0.009 1634 2 0.10 0.003 0.010 1640 3 0.10 0.002 0.013 1653 4 0.14 0.004 0.003 1627 5 0.11 0.004 0.005 1639 Process requirements ≥0.10％ ≤0.004％ ≤0.015％ 1620

[0031] Table 3: Auxiliary materials and deoxidizer addition

[0032] Example Ferrosilicon kg Aluminum iron kg Pre-melted refined slag kg Silicon carbide kg 1 70 10 100 25 2 70 10 100 30 3 70 10 100 30 4 70 10 100 20 5 70 10 100 25 Process requirements 5.0~10.0kg / t 0.5~1.0kg / t 5.0~10.0kg / t 2.0~3.0kg / t

[0033] (3) LF refining process: LF refining is performed with argon blowing at the bottom, active lime 10-15 kg / t steel, silicon carbide 3.0-4.0 kg / t steel is added for diffusion deoxidation, and aluminum particles 1.0-2.0 kg / t steel are added; the temperature range of each furnace of molten steel entering the station is 1510-1550°C, and the power is supplied to increase the temperature for 15-20 minutes while slag is made. After the white slag is formed, the LF takes the incoming sample and measures the temperature, the temperature range is 1540-1560°C, according to the composition of the first sample, ferroalloy is added and the corresponding amount of aluminum is added, and the power is supplied for about 20 minutes to take the second sample and measure the temperature at 1580-1630°C, and the composition is adjusted again. The refining time is 50-60 minutes. After the adjustment is completed, the temperature is measured at 1600-1660°C before leaving the station and going to the VD station. Final slag basicity: 3.0-4.5, white slag time is maintained for 20-25 minutes; power supply time is 50-75 minutes. The inlet and outlet compositions of LF refining are shown in Table 4, where the remainder is Fe and unavoidable impurities.

[0034] LF refining inlet and outlet composition table 4

[0035] Furnace No. C Si Mn P S Al Cr Mo V Example 1: Entry 0.17 0.57 0.20 0.007 0.004 0.037 1.45 1.09 0.76 Instance 1 Outbound 0.38 1.04 0.41 0.012 0.001 0.037 5.13 1.39 0.99 Example 2: Station entry 0.19 0.51 0.16 0.012 0.006 0.034 2.67 1.07 0.89 Instance 2 Outbound 0.39 1.06 0.39 0.014 0.003 0.052 5.10 1.41 0.98 Example 3: Station entry 0.20 0.53 0.22 0.005 0.004 0.032 2.23 1.10 0.84 Instance 3 Outbound 0.40 1.03 0.39 0.010 0.003 0.029 5.16 1.38 0.96 Example 4: Station entry 0.28 0.51 0.19 0.004 0.010 0.034 2.97 1.17 0.82 Example 4 Outbound 0.39 1.07 0.39 0.014 0.003 0.033 5.17 1.37 1.03 Example 5: Station entry 0.22 0.51 0.26 0.009 0.008 0.019 2.50 0.99 0.81 Example 5 Outbound 0.40 1.09 0.36 0.011 0.002 0.034 5.12 1.40 0.95

[0036] (2) VD vacuum process: The temperature of molten steel entering the station is measured at 1585-1650℃. After the ladle seat reaches the vacuum position, turn on the vacuum pump and connect the argon gas. After reaching a high vacuum degree (<67pa), a cyclic degassing period under high vacuum conditions is carried out, which is guaranteed to be more than 10 minutes. After breaking through the air, the temperature is measured and sampled. After the composition returns, the argon flow rate is adjusted, and soft blowing is carried out for 15-20 minutes. The argon gas is turned off and the static period begins. The static time is 10-20 minutes. The temperature is measured at 1510-1540℃, and the ladle is hoisted to the die casting station.

[0037] (3) Die casting steel process:

[0038] First, the argon gas at the entrance of the center injection pipe is replaced by the casting system 3 minutes before the start of pouring (50-100NL / min), and then the argon blowing at the entrance of the center injection pipe is maintained (flow rate 30-50NL / min). There is an argon isolation device between the ladle water outlet and the center injection pipe pouring port to form an argon ring to surround the steel flow. Finally, a small amount of argon is also sealed at the top of the ingot mold during the steel pouring process (10-30NL / min). The amount of gas should not affect the coverage of the protective slag on the molten steel. The pouring speeds such as ingot casting and riser shrinkage compensation time are shown in Table 5.

[0039] Table 5: Casting speed

[0040]

[0041] (4) Refining slag FeO, finished product P control, gas table 6 of Example 1-5

[0042] Examples Refining slag FeO% Finished Product Oxygen ppm Nitrogen ppm 1 0.39 0.012 25 78 2 0.27 0.014 19 64 3 0.58 0.010 15 61 4 0.53 0.014 18 84 5 0.62 0.010 20 81

[0043] As can be seen from Table 6, the P content of the mold steel is controllable, the (FeO)% content of the slag is low, and the nitrogen and oxygen contents have a good control level for the mold casting of the electric arc furnace.

[0044] (5) Non-metallic inclusion levels of forgings in Examples 1-5

[0045] Table 7

[0046]

[0047] The control level of non-metallic inclusions is not lower than that of forging products with the same steel grade, process and nominal capacity using the iron-addition + EBT electric arc furnace die casting process.

Claims

1. A low-cost green smelting method for hot-working die steel, comprising an electric arc furnace steelmaking process, a refining process and a die casting process, characterized in that: The batching structure of the electric arc furnace steelmaking process is: hydrogen-based DRI 15%~20%, scrap steel 80%~85%, of which 40%~50% of the hydrogen-based DRI is added with the scrap steel, and the remaining hydrogen-based DRI is added to the furnace in batches after entering the oxidation period, so that the final C content of the molten steel is controlled at ≥0.10%, P≤0.004%, S≤0.015%, and finally 0.5~1.0kg / t of carbon powder is sprayed on the slag surface; Refining process: LF outgoing Al is controlled at ≥0.030wt%, S≤0.005wt%.

2. A low-cost green smelting method for hot working die steel according to claim 1, characterized in that: The arc furnace steelmaking process: When the arc furnace is tapping steel, when the furnace body reaches the limit tilting angle, the maximum angle α between the steel tapping channel and the horizontal line is -30 0 .

3. A low-cost green smelting method for hot working die steel according to claim 2, characterized in that: The furnace body's maximum tilt angle is 45 0 .

4. A low-cost green smelting method for hot working die steel according to claim 1, characterized in that: The refining process: relying on SiC and aluminum particles for diffusion deoxidation to form white slag, the white slag period is not less than 20 minutes, the binary basicity of LF refining slag is 3.5-5.5, VD vacuum treatment is 10-12 minutes, and the molten steel is left standing for 10-20 minutes.

5. A low-cost green smelting method for hot working die steel according to claim 4, characterized in that: In the refining process, the amount of SiC added is 3.0-4.0 kg / t, and the amount of aluminum particles added is 2.0-3.0 kg / t.

6. A low-cost green smelting method for hot working die steel according to claim 1, characterized in that: The mold casting process: the surface temperature of the outer wall of the steel ingot mold is greater than 80°C before pouring.

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